Multiple-Input Multiple-Output (MIMO) technology is a technology capable of improving data transmission/reception efficiency using multiple transmit (Tx) antennas and multiple receive (Rx) antennas instead of using a single Tx antenna and a single Rx antenna. A receiver using a single antenna receives data through a single antenna path, but a receiver using multiple antennas receives data through multiple paths. Accordingly, data transfer rate and data throughput may be improved, and coverage may be expanded.
To increase a multiplexing gain of MIMO operation, a MIMO transmitter may receive and use channel state information (CSI) fed back from a MIMO receiver. The receiver may determine CSI by performing a channel measurement using a predefined reference signs (RS) from the transmitter.